This invention relates to a valve seal assembly, particularly for a ball valve which has a spherical rotatable valve head engaged by two axially displaceable valve seat sleeves on diametrically opposite sides of the valve head. Those end faces of the sleeves which are oriented towards the valve head form annular seating faces each carrying a sealing ring for engagement with the curved valve head surface. Further, each sleeve, at a location spaced from the valve head, is closely surrounded by a sealing ring cooperating with a housing wall. This sealing ring--which is preferably made of heat resistant material--is exposed to an axial pressing force and abuts, with an end face, a metal (steel) ring mounted on the sleeve.
A valve of the above-outlined type is disclosed, for example, in German Offenlegungsschrift (application published without examination) No. 2,457,230. The sealing ring surrounding the valve seat sleeve is made, for example, of asbestos. One of the radial faces of the sealing ring abuts the bead of the seat sleeve and the other radial face abuts a metal ring which surrounds loosely the valve seat sleeve and is pressed axially by an annular spring against the sealing ring associated with the valve head.
It is a disadvantage of the above-outlined known construction that no separate pressing force can be applied to the sealing ring surrounding the valve seat sleeve for sealing the space between the sleeve and a cylindrical housing wall surrounding the sleeve. This sealing assembly is designed to be exposed only to the pressure which is simultaneously applied to the seal between the valve head and the valve seat sleeve. Such a sealing pressure cannot be varied from the outside. Further, the known valve construction is not adapted for removal of the valve head without disassembly of the valve housing from the pipeline in which it is installed. For such a removal it would be necessary to shift the valve seat sleeves outwardly to an extent sufficient to clear the path to permit pulling of the valve head upwardly, at least in the open position of the valve.
U.S. Pat. No. 3,653,631 discloses a valve construction which includes a worm gear drive by means of which an axial pressure can be exerted on the seals at the end faces of the valve seat sleeve. For this purpose, the worm gear is designed as a threaded ring which surrounds and threadedly engages the valve seat sleeve. Upon rotation of the worm, whose shaft projects from the housing, the valve seat sleeve is axially displaced, while the threaded ring driven by the worm is prevented from shifting axially. Such a worm gear arrangement, however, is incapable of exerting a pressure on a sealing ring mounted about the valve seat sleeve. Further, the known worm gear arrangement cannot be used in valves having upwardly removable valve balls, Thus, the presence of a conventional worm gear arrangement requires a disassembly of the entire valve housing from the pipe if the valve head is to be removed from the valve.